Breathing apparatus with monitored delivery device

ABSTRACT

A breathing apparatus has a first delivery device for adding a volume of a substance to a gas flow, the delivery device having a gas inlet and a gas outlet. A unit monitors a presence of the substance in a gas downstream the delivery device using a first sensor unit at the gas outlet that provides a first measurement value based on an acoustic property of a gas in a first conduit. A second sensor unit at the gas inlet provides a second measurement value based on an acoustic property of a gas present in the second conduit. A control unit determines the presence of the substance based on the first measurement value or based on a comparison of the first measurement value and the second measurement value.

RELATED APPLICATION

The present application is a divisional application of Ser. No.13/510,046, having a United States filing date of Aug. 30, 2012, thecontent of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains in general to the field of breathing apparatuseshaving delivery devices for delivery of substances via a gas flow to apatient. More precisely, the invention relates to monitoring the properfunction of such delivery devices for safety purposes.

2. Description of the Prior Art

Various delivery devices for substances to be delivered to patientsconnected to breathing apparatuses are known, such as anestheticvaporizers for gasifying liquid anesthetic agents. Breathing apparatusesinclude for instance anesthesia machines, intensive care ventilatorswith added anesthesia capabilities, etc.

An erroneous function of such delivery devices may involve a safetyhazard potentially exposing a connected patient to situations with direconsequences, e.g. when a non-desired amount of the substance should bedelivered to the patient.

Hence, there is a need of controlling the correct or desired function ofsuch delivery devices in the breathing apparatuses.

For instance EP-0545567-A1 discloses a method and apparatus for meteringto a patient an anesthetic vaporized from anesthetic liquid held in aliquid space of a liquid container into a gas space. The anesthetic dosecontained in a gas flow supplied to a patient is determined by thevolume/flow of gas passing through the liquid space, i.e. a traditionalby-pass vaporizer. The dose is adjusted in a manner that the dosage ofanesthetic in a gas intended to be respired by a patient matches adesired dosage and the dosage adjustment of anesthetic contained in agas supplied to a patient is effected automatically whenever the currentdosage differs from a desired value.

However, the apparatus of EP-0545567-A1 needs to determine a desireddosage of anesthetic. Determining a dosage as described in EP-0545567-A1may be regarded being complicated. Hence there is a need for a simplersystem. Further, the apparatus uses either pressure drop based flowmeters, or optical sidestream based measurements systems, which areexpensive and have further drawbacks.

When using pressure drop flow sensors or heat wire anemometers formeasuring gas flow, compensation has to be made for changes in gascomposition.

Optical gas analyzers are good but expensive. Moreover, taking asidestream gas sample from the mainstream involves a time delay for themeasurement due to the transportation time from the sample point to theoptical gas analyzer; the main gas flow is interfered with by drawing asample volume, which itself raises issues where to dispose or feedbackthe sample gas volume after measurement from the optical analyzer;sampling is only based on a small portion of the gas conduit at thesampling point, amongst other disadvantages.

Furthermore the output of sensor units such as a pressure drop basedflow meter or a heat wire based flow meter is depended on both the gasflow and physical properties of the measured gas. Particularly in afault situation, where it is most important to ensure patient safety canboth flow and gas concentration be unknown at the same time when usingsuch sensor units. When relying on such sensor units in breathingapparatuses, the system can therefore not distinguish changes inconcentrations from changes in flow. Thus, there is a need to providealternatives avoiding the aforementioned issues and it would forinstance be advantageous to be able to measure flow and/or concentrationindependently.

Hence, an improved or alternative system for determining the presence ofa substance delivered into a gas flow would be advantageous.

Hence, an improved breathing apparatus would be advantageous and inparticular allowing for increased cost-effectiveness, improvedreliability, versatility, and/or patients safety would be advantageous.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention preferably seek tomitigate, alleviate or eliminate one or more deficiencies, disadvantagesor issues in the art, such as the above-identified, singly or in anycombination by providing a breathing apparatus, a method, and a computerprogram according to the appended patent claims.

According to one aspect of the invention, a breathing apparatus isprovided. The breathing apparatus has at least one delivery device foradding a volume of a substance to a gas flow. The delivery device has insome embodiments a gas inlet, and a gas outlet. The delivery deviceenriches a gas flow with a substance, adding a substance volume,preferably in gas form or in a gasifying form (e.g. injection of aliquid substance evaporating in the gas flow) to the gas flow. Theapparatus further comprises a unit for monitoring a presence of thesubstance in a gas downstream the delivery device. The monitoring unitcomprises a first sensor unit arranged at a first gas conduit at the gasoutlet or downstream thereof. The first sensor unit is adapted toprovide a first measurement value based on at least an acousticproperty, such as a sound velocity related property, of a gas present inthe first gas conduit. The apparatus further comprises a control unitoperatively connected to the first sensor unit, wherein the control unitis arranged to determine the presence of the substance based on thefirst measurement value.

With the presence of the substance detected, embodiments implement thedetection of the substance, or a concentration thereof for ensuring thesafety of the breathing apparatus. A too low or too high concentrationmay be undesired. Alternatively, a non-delivery of a substance may beundesired and needs to be monitored. Suitable action may be initiatedupon detection of an erroneous or non-desired function. For instance, auser may be informed of the potential malfunction. Alternatively, or inaddition, the delivery device may be shut down or bypassed in order tocut off delivery of the substance.

According to another aspect of the invention, a method is provided. Themethod is a method of internally controlling a breathing apparatus. Themethod comprises the step of monitoring a presence of at least onesubstance in a gas downstream a delivery device added to a gas flow,wherein the monitoring comprises providing a first measurement valuebased on at least an acoustic property, such as a sound velocity relatedproperty, of a gas present in a first gas conduit by means of a firstsensor unit arranged at the first gas conduit at a gas outlet of thedelivery device or downstream thereof, and determining the presence ofthe substance based on the first measurement value.

According to yet another aspect of the invention a computer program isprovided. The computer program is storable on a computer readablemedium, for processing by a computer. The computer program comprisescode segments for monitoring a presence of at least one substance in agas downstream a delivery device added to a gas flow. The monitoringcode segments comprise code segments for providing a first measurementvalue based on at least an acoustic property, such as a sound velocityrelated property, of a gas present in a first gas conduit by means of afirst sensor unit arranged at the first gas conduit at a gas outlet ofthe delivery device or downstream thereof, and determining the presenceof the substance based on the first measurement value.

Some embodiments provide for detecting a presence of a desired substancein a gas flow in a breathing apparatus.

Some embodiments provide for a detection of a concentration of a desiredsubstance in a gas flow in a breathing apparatus.

Some embodiments provide for a detection of a too low or too highconcentration of a desired substance in a gas flow in a breathingapparatus.

Some embodiments provide for control of a function of a delivery unitdelivering the desired substance.

Some embodiments provide for suitable action to be initiated or takenupon detection of an erroneous or non-desired function of the deliverydevice.

Some embodiments of the invention provide for an independent measurementof a concentration of a certain gas or substance in a gas mixture andgas flow thereof independently.

Some embodiments provide for such independent measurements at a low costthanks to a simple, but still accurate, sensor unit design.

Some embodiments provide for such measurement while avoiding a pressuredrop in the conduit in which the measured gas flows.

Some embodiments avoid exerting an influence of the gas flow at all, asfor instance no gas turbulence is caused in the conduit, or a mainstreammeasurement is provided without the need for a sample of gas taken fromthe flow.

Some embodiments provide for real time measurements without time delay,which is advantageous as steps can be taken faster than previously oreven immediately for counter acting any faulty conditions detected.

Embodiments provide for main stream measurements avoiding any sidestream related issues, such as where to dispose or feedback a sample gasvolume after measurement.

Embodiments provide for measurements of the gas over the entire crosssection of the conduit in which the measured gas is present.

Some embodiments provide for a compact sensor unit providing both a gasconcentration measurement and a gas flow measurement, which isadvantageous as the total gas delivery is monitored.

Some embodiments provide for fast measurements without having to analyzemultiple properties of a gas mixture with advanced gas analyzers.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic illustrations of a combination of adelivery device and a monitoring unit.

FIGS. 2-4 and 8, respectively, are schematic illustrations of breathingapparatuses having embodiments of a delivery device and a monitoringunit.

FIGS. 5A-5C, respectively are schematic illustrations of threeultrasonic sensor units.

FIG. 6 is a flowchart illustrating an embodiment of the method accordingto the invention.

FIG. 7 is a schematic illustration of a computer program according tothe invention.

FIG. 8 is a schematic illustration of a further embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Specific embodiments of the invention will now be described withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Theterminology used in the detailed description of the embodimentsillustrated in the accompanying drawings is not intended to be limitingof the invention. In the drawings, like numbers refer to like elements.

The following description focuses on an embodiment of the presentinvention applicable to an anesthesia machine and in particular to someembodiments an anesthesia machine having a circle system. However, itwill be appreciated that the invention is not limited to thisapplication but may in some examples or embodiments be applied to manyother breathing apparatuses, including for example intensive careventilators with added anesthesia capabilities, ventilators withnebulizers for medicaments, and humidifiers in applications where dosecontrol is critical, etc.

In FIG. 1A, a schematic illustration of a combination of a deliverydevice and a monitoring unit is shown. The delivery device is arrangedfor adding a volume of a substance to a gas flow. The substance isprovided in gas phase in some embodiments. Alternatively, the substancemay be provided in liquid form and injected into the gas flow, where itgasifies. In some embodiments, the substance may not be entirelygasified at the measurement location. In some embodiments, the substancemay be provided in solid particle form, which is delivered to the gasflow. In all embodiments the substance changes the acoustic propertiesof the gas or gas mixture at the measurement location. The illustrateddelivery device 30 has a gas inlet 31 and a gas outlet 33.

A unit for monitoring a presence of the substance in a gas downstreamthe delivery device 30 has a first sensor unit 40 arranged at a firstgas conduit 41 at the gas outlet 33 or downstream thereof. The firstsensor unit 40 is adapted to provide a first measurement value based onat least an acoustic property, such as a sound velocity relatedproperty, of a gas present in the first gas conduit 41. The aggregatefurther has a control unit 50 operatively connected to the first sensorunit 40, and arranged to determine the presence of the substance basedon the first measurement value.

The monitoring unit may further include a second sensor unit 20 arrangedat a second gas conduit 21 at the gas inlet 31 (FIG. 1A) or upstreamthereof (FIG. 1B), adapted to provide a second measurement value basedon at least an acoustic property, such as a sound velocity relatedproperty, of a gas present in the second conduit 21.

The gas present in the second conduit 21 is to be enriched with thesubstance by the delivery device 30, and then present in the firstconduit 41. The gas either passes the delivery device for enrichmentwith the substance, as illustrated in FIG. 1A, or the substance is addedto the gas on the passage from the second sensor unit 20 to the firstsensor unit 40. The added substance will thus be present in the gasphase at the first sensor unit 40 in some embodiments.

The second sensor unit 20 may be omitted in some embodiments, as will beseen below, depending on the type of the first sensor unit 40. Thesecond sensor unit 20 may be omitted in case the added gas flow volumeand composition thereof is known in the system. Such data may beprovided from other units in the system. An example is given below.However, for the sake of simpler illustration, focus is given todescribing embodiments with a second sensor herein.

By having a first sensor unit 40 located at or in the vicinity of theoutlet 33 of the delivery device 30, the function of the delivery device30 can be monitored and controlled in the fastest possible way. Thisadvantage can also be achieved by having a second sensor unit 20 at orin the vicinity of the inlet 31 of the delivery device 30, as themeasurement values of the first and second sensor units may be comparedas explained below. This is of critical importance for applications withinjection-based delivery of the anesthetic agent in the main stream, aslarge doses could be delivered quickly, but could also be useful forother types of dose delivery devices and other means for dose deliveryvia patient gas.

If a deviation is detected in the delivered concentration of asubstance, the control unit 50 may immediately correct the delivereddose by means of a regulatory loop, and alternatively, or in additionactivate suitable measures such as alerting the user, or shut down orbypass the dose delivery device 30 (not shown) if the detectedconcentration is a potential patient hazard.

With traditional vaporizers operating with a bypass principle for dosedelivery such large deviations in dose concentration cannot occur incase of an eventual error. Hence, the requirements on speed ofmonitoring and regulation do not exist in the same manner as describedabove. Therefore, the traditional way of monitoring dose concentrationsis based on side stream measurements in other parts of the system andnot direct vicinity of the dose delivery device as discussed previously.

In the case two sensor units are used, the composition and quantity ofthe gas flow delivered to the delivery device may also be monitored.Also in this case, deviations in gas composition may be corrected by aregulatory loop, and a user may be alerted if deviations from set valuesare detected.

The control unit 50 may be adapted to detect deviations from desiredconcentrations of the substance at the gas outlet 33 based on knowledgeof the composition of the gas flow to the delivery device at the gasinlet 31. A very fast monitoring and regulation is thus provided. Theconcentration of a substance may be measured indirectly by measuring thechange in acoustic properties of the gas. There is accordingly no needfor specialized gas sensors, and a plurality of different gas mixturesmay be monitored.

Hence, the control unit 50 may be adapted to detect deviations based ona change in an acoustic property of the gas in a first measurementvalue, obtained by a first sensor unit 40, i.e. actual delivered value,from an acoustic property value associated with the gas having thedesired concentration of the substance. In this case, the acousticproperties of the gas having the desired concentration of the substancemay be calculated by the control unit 50, as the expected acousticproperties. The actual acoustic properties of the gas at the gas outlet33 may accordingly be compared with the expected acoustic properties ofthe gas, for fast regulation and monitoring without the need forspecialized gas sensors for each gas in the mixture. The control unit 50may be adapted to calculate an expected acoustic property of the gas atthe gas outlet from knowledge of the gas at the gas inlet 31, such as aflow measurement value, and/or a composition measurement of the gas atthe gas inlet, and/or a volume added by the delivery device 30, wherethe volume have an acoustic property, which can be determined by thecontrol unit 50. The flow measurement value and composition measurementvalue of the gas at the gas inlet may be obtained by integrated sensorsin the gas sources 10, 12, 14, or by a second sensor 20.

The control unit 50 may then be arranged to detect a deviation of anacoustic property of the gas at the gas outlet 33, as obtained by thefirst measurement value, from the expected acoustic property calculatedby the control unit 50. Knowledge about a deviation from the calculatedexpected acoustic properties may then be used to determine if thedelivery device 30 is functioning properly, and moreover regulate thegas flow and/or concentration by a regulatory loop

A more detailed description of the embodiments follows below.

In embodiments, such as described with reference to FIGS. 1-4 and 8,both the first sensor unit 40 and the second sensor unit 20 are time offlight/sound velocity measurement units, such as schematicallyillustrated implementations by sensors 42, 43 or sensor 44 in FIGS. 5A,5B and 5C that are described in more detail below.

The speed of sound through a gas mixture is different through differentcomposed gas mixtures. When a substance is added, this generally altersthe acoustic properties of the gas mixture. The speed of sound is thendifferent with or without the substance. This principle can be used as abasis to detect the presence or absence of a substance in a gas or gasmixture. Moreover, a measurement of a concentration of said substance inthe gas or gas mixture may be determined, e.g. based on a look-up table.Temperature compensation may be provided as described below.

Alternatively, or in addition, a comparison of measurements of the samegas or gas mixture without the substance added and with the substanceadded may be made for determining the presence of the substance orconcentration thereof at the first sensor unit. Temperature compensationmay be provided as described below.

Formula (1) represents the speed of sound c in a gas or mixture of gasesas:

$\begin{matrix}{c = \sqrt{\frac{C_{p}}{C_{v}}\frac{R \cdot T}{M}}} & (1)\end{matrix}$

wherein

c is the speed of sound [m/s]

C_(p) is the specific heat at constant pressure [J/mol K]

C_(v) is the specific heat at constant volume [J/mol K]

R is the ideal gas constant=8.3143 [J/mol K]

T is the absolute temperature [K]

M is the molecular weight [kg/mol]

For a given ideal gas the speed of sound c depends only on itstemperature. At a constant temperature, the ideal gas pressure has noeffect on the speed of sound, because pressure and density, which isalso proportional to pressure, have equal but opposite effects on thespeed of sound, and the two contributions cancel out exactly.

As the temperature in conduits in breathing apparatus may vary, atemperature compensation may be provided to ensure a correct measurementof the sound of speed.

The speed of sound in gas can be detected by sending a sound pulsethrough the gas and measuring the transit time of the sound pulsethrough the conduit in which the gas is located, called the time offlight (TOF) for a sound pulse through the gas or gas mixture. As shownin FIGS. 5A-5C, the sound pulse is generated by a first transducer T1and sent towards a second transducer T2 receiving the pulse. Thetransducer may be piezo crystal based transducers.

Examples for the speed of sound through various gases are given in table1 below.

TABLE 1 approximate speed of sound of pure gases at 25° C., i.e. 298 KGas/vapor c [m/s] Air 346 Oxygen—O₂ 329 Nitrous oxide—N₂O 268 Desflurane127

The measured value by the first or second sensor unit 40, 20 is thus theTOF of a sound pulse through the gas in a conduit at the location of thesensor unit 40, 20. A change in the mixture of the gas causes a changein TOF.

Since substance concentration has a substantial influence on the speedof sound of the gas mixture, there is a great difference in the time offlight between the sound pulses traversing a gas mixture with thesubstance and the sound pulses traversing an equal distance in the gasmixture without the substance. As can be seen from table 1, anestheticagents, given as an example in table 1, differ considerably in soundspeed from other fresh gas components (fresh gas is here the gas to beenriched with the substance, e.g. present at the second sensor unit 20).This allows for a very accurate measurement of the concentration ofanesthetic agents in fresh gas, based on measurements of the acousticproperties of such gas mixtures.

For instance, a substance concentration added by the delivery device 30in the gas can be determined and used by the control unit 50.

The control unit 50 may determine the change in TOF and control unit 50thus determines that a substance is present based on such a relativechange of TOF over time.

Moreover, the degree of change in TOF may be used by control unit 50 toestablish the concentration in the gas mixture, based on changes in theacoustic properties by the added substance.

For instance, when the amount or concentration of fresh gas componentsof air, oxygen and/or nitrous oxide delivered by the gas sources 10, 12,14 before adding the anesthetic agent are known in a breathing apparatus(see e.g. in the embodiment described below with reference to FIG. 4),the concentration of the anesthetic agent added by a vaporizer iseffectively determinable by sensor units measuring the sound of speed ofthe gas composition. Even when the amount or concentration fresh gascomponents of air, oxygen and/or nitrous oxide delivered by the gassources 10, 12, 14 before adding the anesthetic agent is not known (seee.g. in the embodiments described below with reference to FIGS. 2 and3), some embodiments still provide an effective and accurate measurementof the anesthetic agent concentration. In the latter case a secondsensor unit 20 based on acoustic measurement principles is arranged at aconduit before addition of the anesthetic agent is made. The two pointmeasurement allows for differential determination of the concentrationof the added anesthetic agent.

Knowledge of the type of substance or anesthetic agent may be used inorder for the control unit 50 to use the TOF measurement to determinethe concentration of the substance or anesthetic agent.

FIGS. 5A, 5B, and 5C show three exemplary geometries and principles of agas component concentration measurement sensor unit or gas componentidentification sensor unit using e.g. an ultrasound transceiver whichmeasures the time of flight (TOF) for a sound pulse passing through thegas to be identified. An ultrasonic measurement sensor 42 of the type asillustrated in FIG. 5B, i.e. sending sound pulses at an oblique angle inrelation to the gas flow direction, such that pulses travel along oragainst the gas flow in one of the two directions. An ultrasonicmeasurement sensor 43 of the type as illustrated in FIG. 5A, i.e.sending sound pulses in a direction substantially perpendicular to thegas flow direction. FIG. 5C shows a further embodiment of an ultrasonicmeasurement sensor 44, sending sound pulses at an oblique angle inrelation to the gas flow direction. By having the transducers T1 and T2of the sensor 44 in the configuration as shown in FIG. 5c the distancebetween the transducers is reduced, compared to FIG. 5b . This may beadvantageous in case detecting gases with a high acoustic dampening. Thetransducers of the sensors may be piezo crystal based transducers, whichallow for both sending and receiving sound pulses.

Sensor units 20 and 40 may be implemented as ultrasonic measurementsensors 42, 43 as shown in FIGS. 5A, 5B, and 5C.

An ultrasonic measurement sensor 42 of the type as illustrated in FIG.5B, i.e. sending sound pulses at an oblique angle in relation to the gasflow direction, may provide one or more of the following measurementvalues:

1. The gas flow Φ in a conduit 45 by measuring the difference in TOFupstream and downstream relative the gas flow:

Gas flow Φ=k*(Tu−Td)/(Tu*Td), wherein

Tu=propagation time for an upstream sound pulse (against the gas flowdirection 47),

Td=propagation time for a downstream sound pulse (in the gas flowdirection 47), and

k is a constant that depends on the geometrical properties of the flowduct and the position of the transducers.

2. The speed of sound c

c=L*2/(Tu+Td), wherein

L is the distance between the transducers.

The speed of sound c provides for calculation of the molecular weight Mof the gas in the conduit 45 according to formula (1), when compensatedfor gas temperature. Gas temperature is for instance measured with aseparate temperature sensor, or may be based on temperature measurementsmade in the breathing apparatus for other purposes.

3. Attenuation of the sound pulse, i.e. decrease of sound pulseamplitude when travelling through the gas in conduit 45. Different gaseslet pass a different amount of sound energy. Attenuation is determinedfrom the amplitude of the detected pulse that has travelled through thegas.

Monitoring of the function of one or more dosage units or a gas deliveryunit providing the fresh gas to be enriched with the substance deliveredby the delivery unit may then be based on at least one of the followentities, alone or in combination:

1. A difference in gas flow Φ before and after enriching the fresh gaswith the substance. An increase in gas flow when comparing a flowmeasurement between units 20 and 40 indicates that molecules of thesubstance have been added to the fresh gas flow by delivery unit 30, seeFIG. 1:

Φ₁>Φ₂

Temperature of the gas travelling from the second sensor unit 20 to thefirst sensor unit 40 may change on the passage, e.g. in the deliverydevice. In case the gas temperature is different at the location of thefirst unit 40 and the second unit 20, temperature compensation of thegas flow may be made based on local temperature measurements at therespective location in order to achieve accurate measurements.

2. A difference in sound velocity c of the gas mixture (compensated fortemperature at 20 and 40 respectively) between the sensor units 20, 40,i.e. c₂≠c₁, then the molecular weight M has changed between sensor unit20 and sensor unit 40:

M ₁ ≠M ₂

This change in molecular weight is due to the substance added to thefresh gas flow by delivery unit 30.

When adding one or more anesthetic agents, which have a much highermolecular weight than air, oxygen, or nitrous oxide (see table 1), then

M₁>M₂ as measured or determined c₂>c₁

In case the gas temperature is different at the location of the firstunit 40 and the second unit 20, temperature compensation of the gas flowmay be made based on local temperature measurements at the respectivelocation.

3. A difference in attenuation measured at the first sensor unit fromthat attenuation measured at the second sensor unit, is indicative of asubstance added in gas phase by delivery unit 30 to the fresh gas flow.

Considering the above, the following can be applied:

a. The second sensor unit 20 may be omitted in certain embodiments—incase the composition of the fresh gas mixture and/or the gas flow at theposition of the second sensor unit 20 is known. In certain breathingapparatuses, the composition of the gas mixture or the gas flow may beknown, e.g. from an already existing measurement, sensor, flowregulator, etc. E.g. the values set for gas flow and gas composition tobe delivered at inlet 21 may be used for calculations and measurementsaccording to the invention. A second sensor 20 may be advantageous formonitoring the delivered gas mixture in case gas composition and/orconcentration is uncertain. A concentration of certain gases in the gasmixture allows for a calculation of the molecular weight M of the gasmixture components respectively.

b. There is no need to determine or measure the entire range of theabove parameters 1.-3. For instance, if only sound of speed andattenuation are determined, a more simple and compact sensor unitconfiguration measuring perpendicular to the gas flow is sufficient, asillustrated in FIG. 5A.

A plurality of sound pulses may be generated in a series by theactuating transducer of the sensor units. Signal parameters like pulseedge, pulse shape, frequency, number of pulses etc. are adapted to thespecific characteristics of the transducer. Alternatively, a continuoussignal, such as a sine wave, may be provided to actuate the transmittingtransducer. By measuring a phase difference between the sent signal andthe signal received by the receiving transducer, the influence of thegas on the sound signal is detectable and a measurement value similaruseable as TOF explained herein.

Now turning to FIGS. 2-4, some specific embodiments of breathingapparatuses implementing various of the above described aggregates aredescribed hereinafter.

In some embodiments, the first sensor unit is an ultrasonic flow meterbased on bidirectional velocity of sound measurements, as illustrated inFIGS. 5B-C and explained with reference thereto.

As shown in FIGS. 1A and 1B, the control unit 50 is operativelyconnected to the second sensor unit 20, and arranged to determine thepresence of the substance based on a comparison of the first measurementvalue and the second measurement value. The second sensor unit 20 may beomitted as described above, and as shown in FIG. 4.

The control unit 50 of embodiments may be connected to further controlunits of the breathing apparatus, e.g. for taking appropriate actionupon detection of non-desired substance presence or concentrationthereof.

The first sensor unit 40 and the second sensor unit 20 are inembodiments of the same type and the comparison of the first measurementvalue and the second measurement value is based on a difference inmeasurement signals thereof. The difference is a measure for aconcentration of the substance in the gas in the first conduit 41,delivered by the delivery unit 30.

The control unit 50 is in this embodiment, and may be so also in otherembodiments, arranged to compensate for a time delay of a gas whenflowing between the first sensor unit 40 and the second sensor unit 20.The gas may flow in a single mainstream configuration between the twosensor units 20, 40, for instance through the delivery device, as shownin FIG. 1A. Alternatively, the gas may flow in a mainstream and one ormore sidestream between the two sensor units 20, 40. The gas flowpassing the second sensor unit 20 may even reach the first sensor unit40 without passing through the delivery device 30. In the latter case,the substance may be added as such, without a carrier gas, to the gasflow between the two sensor units 20, 40. Substances may for instance beadded in a configuration, as shown in FIG. 1B, e.g. based on a substanceinjector principle.

The time delay of the gas flow between two sensor units 20, 40 may bechosen in dependence of a gas flow rate of the gas when flowing betweenthe first sensor unit 40 and the second sensor unit 20.

The time delay (t2−t1) is suitably chosen such that the control unit 50provides a measure or data based on the comparison of the same gastravelling between the second and first sensor unit. This may be basedon two different time, when the gas is at a first time t1 at theposition of the second gas sensor 20 (without the substance added), andwhen the gas has reached the first sensor unit 40 at a later time t2(with the substance added).

The first sensor unit may be an ultrasonic flow sensor 42 devised toprovide a flow measurement value and a concentration measurement of thesubstance. An ultrasonic flow sensor 42 is schematically illustrated inFIG. 5B.

The control unit 50 is arranged to determine one or more of a quantityof the substance added, a volume of the substance added, or aconcentration of the substance added.

The first and/or second sensor units are devised to substantially notinterfere with gas flow in the conduit when passing the sensor unit. Aturbulence, pressure drop, a time delay necessary for the measurement, asidestream flow taken from the main stream, an interaction changing thechemical composition of the substance, etc. are avoided. Compensation,e.g. necessary for a pressure drop at the measurement location is notneeded.

Alternative delivery devices may be arranged in other configurations,e.g. as an injector device injecting the substance into a gas stream,such as illustrated in FIG. 1B. In this case, the delivery device 30does not need a gas inlet. Delivery of the substance may be accomplishedby a pressurized delivery of the substance into a gas flow in a mainconduit at a delivery point 35. The substance may be directly injectedinto the main conduit, or be delivered with a gas flow from a sidestream delivered into the main stream at a delivery point 35. In thelatter case only, the delivery device has a gas inlet 31, which may besupplied with gas from a branching second conduit 21.

In an embodiment of the invention according to FIG. 2, a breathingapparatus 1 is shown. Fresh gas to be entered into a circle system isdelivered by controllable fresh gas sources, such as a first gas sourcefor air 10, a second gas source 12 for oxygen, and a third gas sourcefor nitrous oxide 14. A desired mixture of these gases may be chosen bya user of the apparatus 1 or automatically adjusted in dependence ofuser settings and other conditions in the breathing circuit, in a knownmanner.

The fresh gas is passing a first sensor unit 20 towards the deliveryunit 30. The delivery unit 30 of the embodiment comprises a firstanesthetic vaporizer 32 and a second anesthetic vaporizer 34. The firstanesthetic vaporizer 32 is arranged to deliver a first anesthetic agent,and the second anesthetic vaporizer 34 is arranged to deliver a secondanesthetic agent. Usually only one of the two vaporizers 32, 34 is inoperation in order to avoid mixtures of the two anesthetic agents. Otherembodiments may have only a single delivery unit or anestheticvaporizer. The vaporizers 32, 34, may each have an associated sensorunit 40 (not shown), i.e. a first sensor unit 40 at outlet of thevaporizer 32, and a first sensor unit 40 at outlet of the vaporizer 34.In this may rapid detection, monitoring, or control of each of thevaporizers 32, 34 may be obtained, as elucidated previously and below.Likewise, a second sensor 20 may associated with each of the vaporizers32, 34, but a single sensor 20 may be sufficient if a single gas isinput to the vaporizers 32, 34.

The gasified anesthetic agent enters the circle system in a fresh gasmixture at entry point 61. Inspiratory check valve 62 and expiratorycheck valve 64 ensure the flow direction in the circle system 7.Expiratory valve 65 is closed during inspiration and controls a releasefrom the circle system, e.g. to an evacuation system 80 or similarduring expiration. A volume reflector 70 may be present in the system.The volume reflector 70 may ensure refilling of the circle system withgas during inspiration, as provided by a controllable gas source 16,usually of an oxygen gas source. Alternatively, a bellow (not shown) isused for circulation of the gas. A ratio of rebreathing is suitableadjusted by a control unit of the breathing apparatus 1, which might bethe control unit 50 or a separate control unit. The ratio of rebreathingis adjusted by suitably controlling fresh gas sources 10-12 and gassource 16 for the reflector during inspiration.

The anesthetic vaporizers 32, 34 have a reservoir for the liquidanesthetic agent from which the volume of the anesthetic agent is addedto the fresh gas flow in a suitable manner, wherein the gas flow entersthe delivery device at the gas inlet and leaves the delivery device withthe substance added to the gas stream at the gas outlet. The gas outletof the delivery device is in fluid communication with a first gas outletof the apparatus to which a patient 60 is connected during certainoperation of the apparatus.

The anesthetic vaporizers 32, 34 are anesthetic delivery devices asknown in the art, including one of an injection vaporizer, or anevaporation vaporizer, for adding the volatile liquid anesthetic agentin gasified form to the fresh gas flow. The vaporized anesthetic agentadds an extra gas flow to the fresh gas flow.

A presence of the anesthetic agent in the gas downstream the deliverydevice 30 is measured as follows. The first sensor unit 40 is arrangedat the first gas conduit 41 at the gas outlet 33 or downstream thereof

The second sensor unit 20, if provided, is in some embodiments anultrasonic sound velocity sensor to provide a second TOF measurementvalue of the fresh gas provided by fresh gas sources 10, 12, 14 presentin the first gas conduit (41). The gas has a known composition, e.g. aknown oxygen content and/or nitrous oxide content adjusted by the freshgas sources 10, 12, 14. The gas at the first sensor unit 40 will havethe same composition with regard to these components as it is carried tothe first sensor unit 40. It will be understood that the secondmeasurement value will be provided first in time and the firstmeasurement value subsequently when the gas has traveled along the gasconduits to the first sensor 40.

The first sensor unit 40 is an ultrasonic sound velocity sensor toprovide a first TOF measurement value of the gas in the conduit 41,which is enriched with a flow of gasified anesthetic agent.

The control unit 50, operatively connected to the first sensor unit 40and the second sensor unit 20, determines the presence of the anestheticagent as described above by differential measurement, preferably withthe aforementioned time delay compensation for the travel of gas betweenthe measurement points.

The first sensor unit 40 is located at or in the vicinity of the outletof the delivery unit. This allows for a quick detection of the presenceof the anesthetic agent. As previously mentioned this is of criticalimportance for applications with injection-based delivery of theanesthetic agent in the main stream, as large doses could be deliveredquickly.

In this manner, the control unit 50 is adapted to detect an error,deviation, or faulty function in the delivery unit 30 or at least one offresh gas sources 10-14 arranged to provide the fresh gas flow to thegas inlet. This may be based on a detection of a deviation from adesired concentration of the anesthetic agent. The desired concentrationof the anesthetic agent may be based on a user input via a suitable userinterface of the breathing apparatus 1. Alternatively, or in addition,the detection of a deviation may be based on a detection of anysubstance delivered by the delivery unit 30. In the latter case, thecontrol unit may be set to expect a delivery of a detectable amount ofthe substance by the delivery unit 30. In the case, no delivery of asubstance is detected, suitable action may be activated or taken. Thismay be implemented by having both a first sensor unit 40 and a secondsensor unit 20, and detecting a difference in the measurement signal ofthe both sensor units.

Upon detection of erroneous values, the control unit 50 may alert theuser suitably. Alternatively, or in addition, suitable measures may betaken in the apparatus 1, e.g. shut down/blocking the delivery unit oractivation of a gas flow bypass conduit for bypassing the delivery unit30 with fresh gas upon detection of a concentration of the substancethat is higher than a desired concentration. Alternatively, or inaddition, the dose of anesthetic agent may be adjusted immediately tothe desired value by a regulatory loop.

The control unit 50 may be adapted to detect aforementioned deviationbased on a change in an acoustic property of the gas at the gas outlet33, as provided by the first measurement value, from an acousticproperty value associated with the gas having the desired concentrationof the substance. Hence, a faulty function of the control unit may bedetected by comparing the actual acoustic properties of the gas at thegas outlet 33 with the expected acoustic properties of the gas havingthe desired composition and/or gas flow.

The control unit 50 may be adapted to determine an expected acousticproperty of the gas at the gas outlet 33 from a flow measurement valueand/or a concentration measurement of the substance of the gas at thegas inlet 31. The control unit 50 may be provided with data about thegas composition and/or gas flow of the gas before passing the deliverydevice 30, and data about the desired concentration of the substance inthe gas at the gas outlet 33, and thereafter calculate the expectedacoustic properties of the gas at the gas outlet 33 based onaforementioned data, which data may be provided by an integrated sensorunit in the gas sources 10-14 or by a second sensor unit 20.Subsequently, the control unit 50 may be arranged to detect a faultyfunction in the delivery device 30 by detection of a deviation of anacoustic property of the gas at the gas outlet 33, as provided by thefirst measurement value, from the calculated expected acoustic propertyat the gas outlet 33.

In all embodiments, the possibility to generate an alarm if themeasurement values indicate that the identified gas composition deviatesfrom the gas composition the user has chosen, or if no gas isidentified, increases the overall safety of the breathing apparatus. Adisplay on the user interface facilitates the understanding of what isgoing on in the system.

A further breathing apparatus 2 having an embodiment of the invention isillustrated in FIG. 3. Similar elements are shown as in the embodimentof FIG. 2. However, the first sensor unit is an ultrasonic flow sensor42 of the specific type as shown in FIG. 5B.

The flow sensor 42, as shown in FIG. 5B, is primarily arranged tomeasure gas flow. The transit time for sound pulses Tu respectively Tdare measured, as explained above. The flow is equal tok1*(Tu−Td)/(Tu*Td). Secondly, the TOF is determined from that mean valueof Tu and Td, (Tu+Td)/2, as the sound of speed is inversely proportionalto the TOF. In case the speed of sound c and the temperature T at themeasurement location of the sensor unit are known, the admixture of aspecific gas into a known gas mixture can be determined.

In another breathing apparatus 3 implementing an embodiment of theinvention according to FIG. 4, similar elements are shown as in theembodiment of FIG. 3. However, the second sensor unit 20 is omitted.This is an embodiment where the gas concentrations of components of agas mixture is known at the inlet of the second sensor unit 20, and itis sufficient to only measure the conditions at the first sensor unit40. The effect that a supply of a gaseous substance by delivery unit 30has on e.g. speed of sound or sound attenuation, is sufficient toprovide the above calculations. This could for instance be the case if asingle gas is connected to the inlet of the second sensor unit 20, or ifair is connected to the inlet of the second sensor unit 20. A good gasmixer can give the same conditions and provide the gas concentrations tothe calculation unit 50, as indicated in FIG. 4 by the dotted lineentering the control unit 50 from the direction of the gas sources10-14.

If the flow is known at the inlet of the second sensor unit 20, the flowadded from the delivery unit 30 is calculated by subtracting the flowvalue at the inlet of 20 (unit 20 is non-existent or passive) from themeasured flow at the first sensor unit 40. The second sensor unit 20 maythus be omitted.

A further breathing apparatus 4 having an embodiment of the invention isillustrated in FIG. 8. Similar elements as in the embodiment of FIG. 2have the same reference numerals. The apparatus 4 is for instance anopen system anesthesia machine, i.e. without a circle system forre-using exhaled gases during subsequent inhalations, or an intensivecare ventilator, where exhaled gases are disposed after exhalation. Asubstance is added to the gas flow in inspiratory line 82 and deliveredto the patient 60 during the inspiratory phase of a breathing cycle.During the subsequent expiratory phase exhalation gases from the patient60 are led via expiration line 81 and the expiratory valve 65 from thebreathing apparatus 4.

The substance may be added by the delivery device 30 to an intermittentgas flow or a continuous gas flow. The measurement unit of embodimentsof the invention is adapted to provide the aforementioned measurementsboth for intermittent delivery and continuous delivery.

An intermittent delivery may occur in embodiments of the type describedwith reference to FIGS. 2-4 as fresh gas may only be delivered to thebreathing circuit during an inspiratory phase and/or when re-filling thebreathing circuit with fresh gas, depending on the mode of operation ofthe breathing apparatus 1-3.

An intermittent delivery may occur in embodiments of the type describedwith reference to FIG. 8, or for instance in a breathing circuitaccording to WO2010081914, as inspiratory gas may only be delivered tothe patient during an inspiratory phase. In addition, a continuousbypass flow may be provided from the gas sources 10,12, passing thedelivery device towards the expiratory valve, both during theinspiratory phase and the expiratory phase, e.g. in order to detecttriggering of a new inspiratory phase by the patient via a gas flowtrigger, which is known to the skilled person. In the latter case, thesubstance is delivered continuously, even though not the entire amountthereof is delivered to the patient 60 at all times.

During intermittent delivery, i.e. a temporary stop occurs in the gasflow to which the substance is added, either through the delivery device(see FIG. 1A) or in the main stream (see FIG. 1B). This stop time istaken into consideration when calculating the above described time delayfor the gas passage from the second sensor unit 20 to the first sensorunit 40.

The measurements described above are also provided during continuousdelivery of the substance.

FIG. 6 is flowchart illustrating a method 5 of internally controlling abreathing apparatus, such as the apparatuses 1, 2, 3, or 4 describedabove. The method 5 includes monitoring 100 a presence of at least onesubstance in a gas downstream a delivery device 30 added to a gas flow.The monitoring comprises providing 110 a first measurement value basedon at least an acoustic property, such as a sound velocity relatedproperty, of a gas present in a first gas conduit 41 by means of a firstsensor unit 40 arranged at the first gas conduit 41 at a gas outlet 33of the delivery device 30 or downstream thereof, and determining 120 thepresence of the substance based on the first measurement value.

FIG. 7 is a schematic illustration of a computer program 52 that isstored on a computer readable medium 51, for processing by a computer,such as the control unit 50. The computer program 52 comprises codesegments for monitoring 53 a presence of at least one substance in a gasdownstream a delivery device 30 added to a gas flow, wherein themonitoring comprises code segments for providing 54 a first measurementvalue based on at least an acoustic property, such as a sound velocityrelated property, of a gas present in a first gas conduit 41 by means ofa first sensor unit 40 arranged at the first gas conduit 41 at a gasoutlet 33 of the delivery device 30 or downstream thereof, anddetermining 55 the presence of the substance based on the firstmeasurement value.

The present invention has been described above with reference tospecific embodiments. However, other embodiments than the abovedescribed are equally possible within the scope of the invention. Thedelivery devices may in some embodiments for instance be a humidifierunit for adding water vapor, or a nebulizer unit for adding droplets ofthe substance to the gas stream. Different method steps than thosedescribed above, performing the method by hardware or software, may beprovided within the scope of the invention. The different features andsteps of the invention may be combined in other combinations than thosedescribed.

Although modifications and changes may be suggested by those skilled inthe art, it is the intention of the inventors to embody within thepatent warranted heron all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

We claim as our invention:
 1. A breathing apparatus comprising: adelivery device comprising a gas flow conduit assembly wherein a volumeof a substance to a gas flow in a main conduit of the assembly at adelivery point; a substance monitor configured to monitor a presence ofsaid substance in said gas flow downstream the delivery point, saidsubstance monitor comprising; a first acoustic property sensor unitsituated downstream the delivery point that emits a first acoustic gasproperty measurement value, and a second acoustic property sensor unitsituated upstream the delivery point that emits a second acoustic gasmeasurement value; and a control processor operatively in communicationwith said first sensor unit and said second sensor, and configured todetermine the presence of said substance based on said first measurementvalue and said second measurement value, said control processor alsobeing configured to provide a regulatory loop for a gas compositionincluding said substance added by said delivery device.
 2. The apparatusof claim 1, wherein said control processor is configured to regulate aconcentration of said substance in said gas flow by said regulatoryloop.
 3. The apparatus of claim 1, wherein said control processor isconfigured to regulate a gas flow by said regulatory loop.
 4. Theapparatus of claim 1, wherein at least one of said first acousticproperty sensor and said second acoustic property sensor is configuredto measure a property of said substance related to sound velocity. 5.The apparatus of claim 4, wherein said at least one of said first andsecond acoustic property sensors is configured to execute atime-of-flight measurement of a sound pulse in order to measure saidproperty related to the sound velocity of said substance.
 6. Theapparatus of claim 1, wherein said control processor is configured toadjust a delivery of said substance if a deviation from an expected gasproperty is detected.
 7. The apparatus of claim 1, wherein said controlprocessor is configured to detect a deviation from a desiredconcentration of said substance.
 8. The apparatus of claim 1, whereinsaid control processor is configured to detect at least one of an error,deviation, or faulty function in the delivery device.
 9. The apparatusof claim 1, wherein said control processor is configured to detect atleast one of a malfunction of said delivery device or a deviation ofsaid substance in said delivery device from a desired concentration ofsaid substance, based on data provided to the control processor of thecomposition of said gas flow at said delivery point.
 10. The apparatusof claim 9, wherein said control processor is configured to detect anerror in said delivery device or at least one gas source that providessaid gas flow at said delivery point, by detection of a deviation from adesired concentration of said substance.
 11. The apparatus of claim 9,wherein said control processor is configured to detect said deviationbased on a change in an acoustic property of said gas in said firstmeasurement value from an acoustic property value associated with saidgas having said desired concentration of said substance.
 12. Theapparatus of claim 1, wherein said control processor is configured tocease operation of said delivery device upon detection of aconcentration of said substance that is higher than a desiredconcentration.
 13. The apparatus of claim 1, wherein said controlprocessor is configured to activate the regulatory loop for adjustmentof said concentration of said substance to said desired concentrationupon detection of an error in operation of said delivery device.
 14. Theapparatus of any of claim 1, wherein said control processor isconfigured to calculate an expected acoustic property of said gasdownstream said delivery point from at least one of a flow measurementvalue and a composition measurement of said gas upstream said deliverypoint and a volume added by said delivery device, said volume having anacoustic property, and wherein said control processor is configured todetect a deviation of an acoustic property of said gas in said firstmeasurement value from said expected acoustic property.
 15. Theapparatus of claim 1, wherein at least one said first and secondacoustic property sensors is an ultrasonic sensor and is configured tomake at least one measurement selected from the group consisting of agas flow measurement of said substance and a concentration measurementof said substance.
 16. The apparatus of claim 15, wherein at least oneof said first and second acoustic property sensors is configured tomeasure a main stream characteristic of said gas in said main conduit ofsaid assembly or in another conduit of said assembly.
 17. The apparatusof claim 1, wherein said substance is a volatile anesthetic agent, andsaid delivery device is an anesthetic delivery device, comprising avaporizer selected from the group consisting of an injection vaporizerand an evaporation vaporizer that adds said volatile anesthetic agent tosaid gas flow.
 18. The apparatus of claim 1, wherein said first sensorand said second sensor are of the same type and said control processoris configured to detect a difference in said first and secondmeasurement signals thereof.
 19. A method of internally controlling abreathing apparatus comprising monitoring a presence of at least onesubstance in a gas downstream a delivery device added to a gas flow,said monitoring comprising: providing a first measurement value based onat least an acoustic property, such as a sound velocity relatedproperty, of a gas present in a main gas conduit by means of a firstsensor unit arranged at said main gas conduit at a delivery point ofsaid delivery device or downstream thereof; providing a secondmeasurement value based on at least an acoustic property, such as asound velocity related property, of said gas present in said mainconduit by means of a second sensor unit arranged at said main gasconduit at the delivery point or upstream thereof; and regulating a gascomposition including said substance added by said delivery device basedon said first measurement value and said second measurement value.